The current "search query" section has two search fields and looks like this:

Current Advanced Search

i) The Post Search Field

The first search field is a search for posts. It can search for keywords in a post's text and/or title in two ways:

Search for all terms or use query as entered

Search for any terms

Let's look at those two options. As an example query I'll be using the following: dunkin donuts

Option 1: Search for all terms or use query as entered

The first option, which is the default one, will search for all the keywords or the entire phrase (i.e. the sequence of keywords). It is a combination of two searches that we are all familiar with at Google's search. The +keyword search and the search for a phrase:

+dunkin +donuts

"dunkin donuts"

The first query is also valid for phpBB. Typing +dunkin +donuts or dunkin donuts doesn't make any difference when the first option is selected.

Option 2: Search for any terms

With the second option selected, when searching for dunkin donuts, the results that we'll get are the posts that contain at least one of the keywords in its text and/or title. It would be exactly the same if we had used the pipe operator and typed dunkin|donuts.

ii) The Author Search Field

The second search field doesn't make use of any search operators, apart from the wildcard (*). You type a single keyword and it searches for a single author.

iii) Proposal: Combined Search Fields

We could combine the post and author search fields into one, and remove the description for the two search options of the former. The user can still search for any terms by using the pipe (|) operator. So something like this:

Proposed Advanced Search #1 - Single Search Field

Or, something like this:

Proposed Advanced Search #2 - Single Search Field

The user could change between post search and author search by clicking on a dropdown menu:

Proposed Advanced Search #2 - Single Search Field And Menu

Finally, we could use some JavaScript to change the description on the left when switching between post and author (since the author search does not make use of all the operators).

I believe that particular section at the Advanced Search should be made simpler to use, so if you also think the same and/or you believe you have a better idea for the UI please discuss it in this topic (and if you disagree also discuss it here of course).